About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / hw_random.txt




Custom Search

Based on kernel version 3.13. Page generated on 2014-01-20 22:03 EST.

1	Introduction:
2	
3		The hw_random framework is software that makes use of a
4		special hardware feature on your CPU or motherboard,
5		a Random Number Generator (RNG).  The software has two parts:
6		a core providing the /dev/hw_random character device and its
7		sysfs support, plus a hardware-specific driver that plugs
8		into that core.
9	
10		To make the most effective use of these mechanisms, you
11		should download the support software as well.  Download the
12		latest version of the "rng-tools" package from the
13		hw_random driver's official Web site:
14	
15			http://sourceforge.net/projects/gkernel/
16	
17		Those tools use /dev/hw_random to fill the kernel entropy pool,
18		which is used internally and exported by the /dev/urandom and
19		/dev/random special files.
20	
21	Theory of operation:
22	
23		CHARACTER DEVICE.  Using the standard open()
24		and read() system calls, you can read random data from
25		the hardware RNG device.  This data is NOT CHECKED by any
26		fitness tests, and could potentially be bogus (if the
27		hardware is faulty or has been tampered with).  Data is only
28		output if the hardware "has-data" flag is set, but nevertheless
29		a security-conscious person would run fitness tests on the
30		data before assuming it is truly random.
31	
32		The rng-tools package uses such tests in "rngd", and lets you
33		run them by hand with a "rngtest" utility.
34	
35		/dev/hw_random is char device major 10, minor 183.
36	
37		CLASS DEVICE.  There is a /sys/class/misc/hw_random node with
38		two unique attributes, "rng_available" and "rng_current".  The
39		"rng_available" attribute lists the hardware-specific drivers
40		available, while "rng_current" lists the one which is currently
41		connected to /dev/hw_random.  If your system has more than one
42		RNG available, you may change the one used by writing a name from
43		the list in "rng_available" into "rng_current".
44	
45	==========================================================================
46	
47		Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
48		Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
49		Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
50	
51	
52	About the Intel RNG hardware, from the firmware hub datasheet:
53	
54		The Firmware Hub integrates a Random Number Generator (RNG)
55		using thermal noise generated from inherently random quantum
56		mechanical properties of silicon. When not generating new random
57		bits the RNG circuitry will enter a low power state. Intel will
58		provide a binary software driver to give third party software
59		access to our RNG for use as a security feature. At this time,
60		the RNG is only to be used with a system in an OS-present state.
61	
62	Intel RNG Driver notes:
63	
64		* FIXME: support poll(2)
65	
66		NOTE: request_mem_region was removed, for three reasons:
67		1) Only one RNG is supported by this driver, 2) The location
68		used by the RNG is a fixed location in MMIO-addressable memory,
69		3) users with properly working BIOS e820 handling will always
70		have the region in which the RNG is located reserved, so
71		request_mem_region calls always fail for proper setups.
72		However, for people who use mem=XX, BIOS e820 information is
73		-not- in /proc/iomem, and request_mem_region(RNG_ADDR) can
74		succeed.
75	
76	Driver details:
77	
78		Based on:
79		Intel 82802AB/82802AC Firmware Hub (FWH) Datasheet
80			May 1999 Order Number: 290658-002 R
81	
82		Intel 82802 Firmware Hub: Random Number Generator
83		Programmer's Reference Manual
84			December 1999 Order Number: 298029-001 R
85	
86		Intel 82802 Firmware HUB Random Number Generator Driver
87		Copyright (c) 2000 Matt Sottek <msottek@quiknet.com>
88	
89		Special thanks to Matt Sottek.  I did the "guts", he
90		did the "brains" and all the testing.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.